1. Field of the Invention
The present invention relates to such hydraulic machines that include a screw array in the form of a drive screw and one or more running screws mounted in a housing, and implemented such that the screws seal against each other and the housing, while forming chambers which are displaced axially along the screw array during the rotation of the screws. The machine may work as a pump if the drive screw is driven by a motor, liquid being conveyed from the low pressure side to the high pressure side in the chambers formed by the screws and housing, or as a motor, liquid then being fed to the high pressure side and as it moves in the chambers to the low pressure side it drives the screws, so that the drive screw can drive an apparatus coupled to its shaft.
The screw array and housing are arranged in an exterior housing through which the drive screw shaft situated at the high pressure end extends under the intermediary of a seal. The drive screw shaft is provided with a balancing piston for balancing a part of the axial force acting on the screw, and also with a washer or collar which together with a wall portion of the housing forms a hydrostatic axial bearing for taking up the remaining axial force acting on the drive screw.
2. Description of the Prior Art
Hydraulic machines of the kind mentioned above are already known, e.g. from U.S. Pat. No. 4,131,400 to Segerstrom, issued Dec. 26, 1978. A disadvantage burdening the machine according to this published specification is that the radial mounting of the shaft on the high pressure side of the drive screw is unsatisfactory, particulary if the machine is driven by a motor, the shaft of which is not exactly in register with the shaft on the drive screw, since the plain bearings used in the machine have a limited ability of taking up forces from such misalignment. Another disadvantage is that the axial bearing arrangement for the shaft has also been unsatisfactory, particularly if the machine pumps cold oils and/or oils under low pressure, since oil is then not capable of penetrating into the gap defined by radial bearing surfaces on a part of the housing and a collar fastened to the shaft adjacent the balancing piston, resulting in large wear on the bearing surfaces. Further disadvantages are that the machine cannot be started with a large inlet pressure, since the mentioned collar will then engage with great friction against a sleeve attached to the other side of said housing part and cause wear on both these parts. In extreme cases parts of the machine such as the collar can even be destroyed.